Alternative spawning tactics of female angelfish according to two different contexts of sex change

Social conditions for sex change and reproductive success were studied in the haremic marine angelfish, Centmpjgt ftrrugatus, in the coral reefs of southern Japan. In this species the largest female in a harem changed sex not only after disappearance of the dominant male but also occasionally in his presence. In isolated harems containing two to three females, strict social control by the dominant male resulted in females rhanging sex only after the male disappeared (takeover sex change). In harems adjacent to each other, however, takeover sex change did not occur even when one of the males disappeared. Instead, large harems including more than four females were formed by fusion of two adjacent harems. In such large harems, the dominant male was unable to socially prevent the largest female from changing sex later to acquire a portion of the harem (harem-fission sex change). Females in adjacent harems spawned less frequently and tended to grow faster than those in isolated harems, probably to gain an advantage in dominance status over neighbors of similar size. Thus, females changed spawning frequencies according to the two different contexts of sex change. The takeover tactic results in higher fitness than the harem-fission tactic, which should be the best in the bad situation of adjacent harems.